Nickel Alloy X750 Powder

Processing and Manufacturing

Nickel Alloy X750 powder can be processed into finished components using various methods:

Casting

• Investment casting is commonly used. Ceramic molds enable pouring at 2600-2800°F (1427-1538°C). Produces highly sound castings.
• Sand casting can also be done but extra feeding of liquid metal is needed to get soundness. Special sand binders may be required.
• Shell mold casting yields products comparable to investment cast. Thin rolls can be produced.
• Continuous casting in graphite molds is widely used for producing billets for further processing.

Table 11: Casting specifications

Typical casting defects like hot tears, microporosity and segregation can occur but can be minimized by proper gating/risering, mold design and pouring/shakeout practices.

Deformation Processing

Hot working is performed between 2150-2300°F (1177-1260°C) followed by air cooling. Warm working is done below 1900°F (1038°C). Cold working may require intermediate annealing.

Common methods include:

• Forging: Closed die process produces best properties
• Rolling: Both flat and shape rolling performed. Minimum thickness reduction 30%
• Extrusion: Excellent properties achieved in sections up to 8 in dia
• Drawing: Heavy wire/bar can be drawn. Intermediate softening may be needed.

Table 12: Key specifications

Joining Processes

All standard methods can effectively join X750 parts. Matching alloys preferred for optimum properties.

Welding: Gas tungsten arc (GTAW) and gas metal arc welding (GMAW) most widely employed. Resistance and laser beam welding also occasionally applied. Matching composition filler rods are used. Joints exhibit excellent strength. Proper preheat and post weld heat treatment essential to avoid cracking.

Brazing: Vacuum brazing gives best combination of strength and temperature resistance. Various silver braze alloys used with brazing done at 1900-2000°F (1038-1093°C). Critical to control clearances, fluxes and atmosphere.

Table 13: Joining recommendations

Post Processing Treatments

Solution heat treating and age hardening are used to develop optimum properties:

Solution Treatment – Performed at 2100-2300°F (1149-1260°C) followed by air or water quenching. Enables subsequent age hardening.

Age Hardening – Age at 1325-1425°F (± 25°F) for 10-50 hours followed by air cooling. Achieves precipitation hardening for maximum strength levels.

Optional stabilization treatment involves 850-1200°F for 1-16 hours to stabilize against future property changes.

Table 14: Post processing specifications

Powder Production

Nickel Alloy X750 powder is commercially produced by gas atomization and water atomization methods. Particle size distribution tightly controlled through specialized nozzles and calibrated sieving. High purity inert gas used to prevent contamination.

Table 15: Powder production methods

Both gas and water atomized powders show spherical particle morphology ideal for additive manufacturing, metal injection molding and other powder metallurgy applications.

Design Data

Key design data parameters for Nickel Alloy X750 are summarized below for reference during engineering and component design activities:

Table 16: Design data parameters for Nickel Alloy X750

Structural Load Conditions

For structural engineering calculations at temperature extremes, use:

• Tensile yield strength: 140-190 ksi
• Compressive yield strength: 170-220 ksi
• Modular ratio, E (Alloy X750)/E (Steel): 1.0

At room temperature up to 500°F – Moderate corrosion rate of less than 0.002 in/yr expected.

Up to 1900°F – Excellent resistance to hot corrosion and oxidation. Use parabolic rate constant kp = 3.4 x 10-8 mg2/cm4/s.

Creep and Fatigue Resistance

Alloy X750 demonstrates excellent creep resistance. Rupture strength higher than 80 ksi for 100,000 hrs at 1300°F (980°C).

For cyclic fatigue conditions, use:

• Endurance (106 cycle) fatigue strength of 95-100 ksi
• Reduction factor of 1.0 for machined surface finish rather than as-fabricated

Environment has small effect on fatigue strength. Use fatigue reduction factor = 0.95 for air environment.

Machining Nickel Alloy X750

Nickel Alloy X750 has excellent machinability in the annealed state and can be machined using most standard workshop methods and tools.

Chip breakers recommended for effective chip control. Rigid setups needed to minimize vibration. Positive rake cutting tools with sharp cutting edges provide longest tool life.

Low thermal conductivity leads to heat concentration so copious coolant should be used.

Table 17: Machining methods

Processing and Manufacturing

Nickel Alloy X750 powder can be processed into parts using various methods:

Additive Manufacturing

Additive manufacturing (AM), also known as 3D printing, uses the nickel alloy powder as feedstock for building up components layer by layer. Some AM techniques suitable for X750 include:

Direct Metal Laser Sintering (DMLS)

• Powder is selectively melted by a high power laser
• Produces fully dense parts with fine microstructure
• Excellent dimensional accuracy and surface finish
• Complex geometries possible

Electron Beam Melting (EBM)

• Powder is melted by an electron beam in vacuum
• Achieves near full density with good strength
• Lower surface finish compared to laser processes
• Fast build rates due to higher beam power

Binder Jetting

• Liquid bonding agent selectively deposited to join powder particles
• Cost-effective process with high productivity
• Requires post-processing like sintering and infiltration
• Larger parts possible with good geometric freedom

Cold Spray

• Powder particles accelerated to supersonic speeds and impacted on to a substrate
• Kinetic energy bonds particles to surface
• Thick coatings and freeform shapes can be built up
• Minimal heating preserves base material properties

Table 11: Additive manufacturing processes for Nickel Alloy X750

Parameters like laser power, beam size, hatch spacing, and scanning strategy can be optimized to control part density, surface quality, microstructure and mechanical performance.

Heat treatments like hot isostatic pressing (HIP) and aging may be applied post-processing to further enhance densification and material properties.

Casting

The X750 alloy can also be induction melted and cast into ingots, billets and bars using processes like:

• Vacuum induction melting
• Electroslag remelting
• Investment casting

Cast products serve as feedstock for subsequent breakdown operations like forging, rolling and extrusion. They can also be machined directly into net shape components.

Deformation Processing

Various deformation techniques can be applied to cast nickel alloy feedstock:

Forging

• Pressing or hammering cast ingots between dies
• Improves strength through grain flow and work hardening
• Near net shapes can be achieved

Rolling

• Compressing and reducing thickness between rolls
• Produces sheets, strips and plates
• Controls grain structure and enhances properties

Extrusion

• Forcing through a die opening
• Forms long sections with fixed cross-section
• Dense product with uniform fine grains

Drawing

• Pulling through a die using tensile force
• Reduces cross-section of bars, tubes or wires
• Increased strength and hardness

The alloy is annealed periodically during working to restore ductility and avoid cracking. Final heat treatment and aging follows to achieve desired characteristics.

FAQs

Q: What is Nickel Alloy X750?

A: X750 is a precipitation-hardenable nickel-chromium alloy with excellent strength up to 1300°F (700°C), outstanding corrosion and oxidation resistance, and good fabrication characteristics.

Q: What are the typical applications for X750?

A: Gas turbines components, turbocharger parts, nuclear fuel elements, chemical processing equipment, food processing vessels – anywhere needing capability at high temperatures in harsh environments.

Q: Is Nickel Alloy X750 weldable?

A: Yes, X750 has good weldability for a high-strength precipitation-hardened alloy. Gas tungsten arc and gas metal arc welding can produce sound welds. Stress relieving heat treatment is often employed after welding.

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